1. Field of the Invention
The present invention relates to a zoom lens suitable for a television camera, a cinema camera, a video camera, a film camera, or a digital camera, and more particularly, to a zoom lens having high magnification, reduced size and weight, and high performance, and an image pickup apparatus including the same.
2. Description of the Related Art
A small and lightweight zoom lens having a wider angle of view, a higher zooming ratio, and higher optical performance has been demanded for an image pickup apparatus such as a television camera, a cinema camera, a film camera, or a video camera. In particular, image pickup devices such as a CCD and a CMOS, which are used in the television or cinema camera as a professional video photographing system, have a substantially equal resolution over the entire image pickup range. Therefore, the zoom lens using the image pickup device is required to have a substantially equal resolution from a center to a periphery of the screen, and required to be small and lightweight to support photographing modes that put a high priority on mobility and operability. In addition, in recent years, in order to obtain visual expression utilizing a shallow depth of filed and high sensitivity, a camera including a large-sized image pickup device has been developed, and a zoom lens responding to this camera has been demanded.
Hitherto, the following zoom lens has been known as a zoom lens having high magnification, reduced size and weight, and high optical performance. The zoom lens employs an inner-focusing system and includes, in order from an object side, a first lens unit having a positive refractive power that is fixed during zooming, a second lens unit having a negative refractive power that moves during the zooming, a third lens unit having a negative refractive power, for correction of an image plane, an aperture stop, and a lens unit having a positive refractive power that is fixed during the zooming. The first lens unit includes a first sub-lens unit having a negative refractive power, a second sub-lens unit having a positive refractive power, and a third sub-lens unit having a positive refractive power. The second sub-lens unit takes a role of the focusing.
For obtaining the high magnification, the reduction in size and weight, and the high performance in the zoom lens described above, the refractive powers and the structures of the lens units need to be appropriately set.
Each of zoom lenses disclosed in U.S. Pat. No. 5,757,554 and Japanese Patent Application Laid-Open No. 2004-341237 has a structure optimal for a camera including a relatively small image pickup device for a television camera, and hence has a problem in that the zoom lens is increased in size when being applied to a camera including a large-sized image pickup device.